Cause and Prevention of Spalling of Backup Rolls for Hot Strip Mill

Spalling phenomena of the backup rolls used for hot strip mills and their prevention are discussed. The spalling on the surfaces of backup rolls is classified into two categories: excess rolling contact fatigue resulting from the local wear in roll barrel and propagation of the surface cracks generated by thermal shock in the mill accidents such as squeezing and roll slip, and also by incomplete removal of the cracks in roll dressing. Factors for preventing the spalling phenomena are studied from the experiments in both production mills and laboratory. The spalling tendencies are correlated with the carbon and chromium contents, areal fractions of carbides, and fracture toughness values of roll materials. To prevent the spalling, therefore, it is necessary to control and improve both properties of roll materials and procedures of roll maintenance.